Air pollution: Cloud seeding is not the solution

Cloud seeding is the process of artificially inducing rainfall. To provide relief from air pollution in Delhi after Diwali, the Delhi government, in collaboration with IIT-Kanpur, conducted cloud seeding on October 28. Due to atmospheric heat, water from oceans, rivers, lakes, and other water bodies evaporates into vapor. The process of converting vapor into liquid droplets is called condensation while the direct transformation of vapor into a solid is called deposition. Condensation occurs with the help of tiny particles suspended in the air. Examples include dust particles, other small particles, or volcanic ash. These tiny particles act as condensation nuclei. Water vapor gathers around these particles (condensation nuclei) and transforms into liquid droplets or ice crystals.

When many such liquid droplets or ice crystals accumulate, a cloud is formed. As the size and weight of these droplets or ice crystals increase, they fall to the earth as rain. This is how natural rainfall occurs.

Cloud seeding:

Clouds can naturally produce rain. But not all clouds result in rainfall. In cloud seeding, chemicals like silver iodide, dry ice, or salt act as artificial condensation nuclei. These substances are released into moisture-laden clouds using aircraft, rockets, or ground-based generators. The nuclei help form sufficient liquid droplets or ice crystals, increasing their size and weight, thereby inducing artificial rainfall. Like a car with a working engine and fuel that may not start due to a weak battery and needs a push, cloud seeding works when clouds and sufficient moisture are present, but rain does not occur naturally.

Clouds may not always produce rain:

Cloud seeding does not work under clear skies. Insufficient number of condensation nuclei to convert water vapor into droplets or ice crystals. Cloud seeding aims to address such critical issues.

How can human activities affect clouds?

Research shows that aerosols released into the atmosphere due to air pollution affect cloud formation and can inhibit rainfall. Aerosols prevent water droplets in clouds from merging into larger, heavier droplets. As a result, the droplets remain very small and continue to float in the atmosphere. Thus, air pollution from urban and industrial activities significantly impacts rainfall patterns.

Why the experiment failed in Delhi?

Cloud seeding works only when clouds have around 50 per cent or more humidity. However, in the Delhi experiment, the targeted clouds had only 15–20 per cent humidity, according to Manindra Agrawal, Director of IIT, Kanpur, which partnered with the government for the project. He stated that a chemical mixture of common salt, rock salt, and silver iodide was used.

According to the Indian Institute of Tropical Meteorology, although cloud seeding trials are usually conducted for drought management, this was the first indigenous attempt to use the method for air pollution control, Agrawal noted.

Where has cloud seeding worked?

Over 50 countries, including Saudi Arabia, the United States, Israel, Indonesia, and Australia, have conducted cloud seeding projects at some point. Some achieved good results, while others saw little or no success.

The United Arab Emirates (UAE) is noted as one of the most successful countries in cloud seeding. It conducts operations annually to increase rainfall and combat severe water scarcity. Reports indicate rainfall increased by 10 to 30 per cent in some areas.

China’s success:

During the 2008 Beijing Olympics, China successfully used cloud seeding to create favourable weather conditions. To prevent rain during the opening and closing ceremonies, clouds were “emptied” in advance. China launched over 1,100 rockets from several locations, using silver iodide for cloud seeding. This subsequently delayed rainfall in Beijing and resulted in clear skies.

Adverse effects:

Cloud seeding can interfere with naturally occurring rainfall. The chemicals used may alter the concentration of other atmospheric gases. Artificially inducing rain in one area can disrupt weather balance in nearby regions, potentially reducing rainfall nearby. In some cases, cloud seeding has led to sudden heavy rainfall, resulting in floods.

Scientists warn that cloud seeding is not a permanent solution to Delhi’s air pollution. While it may provide short-term relief, it does not address the root causes of pollution. Even if artificial rain is successful, it may clear the air for only a few hours or days—a temporary fix. Therefore, it is important to implement long-term strategies to tackle air pollution.

(The writer is a Chemistry and Environmental Sciences faculty)